Due to vehicle/train and person/train collisions, by federal law and or regulation, all trains must sound their horns at a track/road intersection: two long blasts, one short blast, and then another long blast. The total blast sequence is 15-25 seconds in duration depending on the speed of the train.
When some people hear that whistle blowin', they hang their head and cry. Due to the annoyance train horn sounding causes people in homes, businesses, and abutting properties or in close proximity to the track/road intersection, federal regulations also prescribe that the sounding sequence must start no sooner than one-quarter mile from the intersection and cease when the lead locomotive passes through the intersection.
Still, given that the regulations still mandate an amplitude of 96-110 A-weighted decibels (dBA) 100 feet forward of locomotive, the currently omni-directional train horn sounding sequence still causes annoyance to people in homes, business, and abutting properties or in close proximity to train/road intersections. See generally U.S. published application No. 2007/0102591 incorporated herein by this reference.
The '591 patent application proposes a narrow beam acoustic emitter located at train/road crossings, oriented parallel to the road, and triggered at a time based on the speed of the train and the time it will reach a predetermined point.